Circuit breaker



- Aug. 1, 1939.

G. A. MATTHEWS CIRCUIT BREAKER Filed Nv. 5, 19:54

3 Sheets-Sheet 1 a 1, 93 G. A. MATTHEWS 2,167,665

CIRCUIT BREAKER 7 Filed Nov. 5, 19 34 3 Sheets-Sheet 2 J? 65 3i 6 "Q; Ib 6 1 5 'l 156 lll 5i V 36 W O I l 7 1, 1939? cs. A. MATTHEWS 2,167,665

- CIRCUIT BREAKER:

- Fiied Nov. 5. 1954 s Sheets-Sheet s M gg.

Patented Aug. 1, 193 9 PATENT OFFICE 2,167,865 omcm'r BREAKER George A.Matthews, Detroit, Mien, miraclto The Detroit Edison Company, Detroit,Mich; a corporation of New York Application November 5, 1934, Serial No.751,511 13 Claims. (Cl. 200-149) 10 carrying an arc is conductingbecause it is ionized;

that is, because a considerable number of normally electricallyneutralized molecules are broken up into electrically charged partscalled ions. If the-arc is to be extinguished and, if the gas is to llrecover its normal insulating state, these ions must disappear. Left toitself, the ions, in the ionized gas disappear spontaneously by direct vrecombination. This process is relatively slow and'is of littlepractical use in the interruption 7 20 of an alternating currentcircuit.

It has been found in this connection that a very I effective means forincreasing the rate of deionization, and hence the more rapidextinguishment of the arc, is to bring the surfaces of Solids 25 closeto the arc in a confined space so that ions may collect thereon andvrecombine there.-

Moreover, there seems to be a great difference p in the effect of thesesurfaces, depending upon whether the surfaces are refractory, or whether30 under the heat of the arc, the surfaces are decomposed givingofilarge quantities of gas. In

the latter case, under proper conditions much higher voltage and higherpower circuits can be interrupted. The increased effectiveness of de- 35composing walls is believed to be due to the rapid evolution of gas; andthe turbulence introduced into the confined are 'by the rapidintermixing of freshly generated un-ionized gas is believed to be anextremely effective means for causing rapid 40 deionization at currentzero.

Tests have shown that, if horn fiber or other organic matter is placedadjacent the are, it will be decomposed; giving ofi relatively largepercentages of hydrogen and carbon monoxide, and a 5 small percentage ofhydrocarbons, which .are particularly eflicacious in the rapiddeionization of the arc and hence its rapid extinguishment.

A great many electrical and mechanical devices have been tried with moreor less success to em- 50 body the foregoing principles in circuitbreakers for interrupting circuits under load. In the main, thesedevices have been too costly to permit being used in any but the mostexpensive installations.

With the foregoing in mind, the present inven- 55 tion seeks to providein a circuit breaker an economical construction embodying the aboveprincipies, and which is so arranged as to not only perform the functionof a circuit breaker to open a circuit under load, but may also be usedas a disconnecting switch to effect a visual gap in the 5 circuit.

A further object of the invention resides in the provision of animproved circuit breaker of the dry-type, thereby lessening explosiveand fire hazards to life and property. I

It is a further object of the invention to provide a circuit breaker orsimple and relatively inexpensive construction and at the same time acircuit breaker having excellent arc extinguishing characteristics. Y

A further object of the invention is to provide a circuit breaker havingparts which are arranged and operative in such a; manner as to enablethe production of a circuit breaker of mate- I rially smaller physicalsize forv a given capacity, than has heretofore been possible.

It is also an object of the hereindescribed invention to provide acircuit breaker of such construction and arrangement of parts as toenable its being embodied into a plurality of arrangements, such forexample, as a single or multiple break circuit breaker, and also invarious combinations with fuses, etc.

In accordance with the general features of the present invention, it isproposed to provide an elongated tube of organic material such as hornfiber within which there is mounted a. contact rod of such size as toprovide a space between the exterior surface of the rod and the interiorsurface of the tube. Contacts are respectively associated with thecontact rod and the tube so that when the rod is moved axially relativeto the tube, the contacts may be moved into or out of engagement. Thereis also provided an extension to the contact rod, this extension beingsimilarly formed of organic'material such as'horn fiber. The extensionis of such lengthv that when the rod is moved in a direction to separatethe contacts, the extension serves as a follower to maintain a constantpredetermined cross-sectional area in the spacewithin the tubebetweenthe follower and the inner wall of the tube. The contacts justmentioned are mounted adjacent oneend ofthe fiber tube so that theresistance to the movement of the arc gases formed by the separation ofthe contacts would be greater in one direction than it would be 'in theother direction as they move through the space between the tube and therod or extension thereon. Due to the fact that there is less resistanceto movement of the arc gases toward the follower or extension of therod, the arc will move in that direction and in so doing will be incontact with the organic material of the tube and also the organicmaterial of the follower or rod extension. Under the heat of the arc,the fiber or other organic material will be decomposed and emitun-ionized gases which will act to assist deionization of the arc andhence its extinguishment. The turbulence caused by the rapid generationof these gases in the confined space also contributes to this result.

As an additional feature of the invention, the rod extension may beextended into a closed container or chamber in communication with theassociated end of the fiber tube. Due to the movement of the rodextension, in opening the contacts, the extension acts as a piston andtends to create decreasedpressurewithin the chamber, this decreasedpressure operating to draw the are through the space between the rodextension and the fiber tube, in a direction toward the. chamher. Thischamber also serves as a relief for the expansion of the gases whichhave been emitted irom the decomposition, of the material in the tubeand contact rod extension.

Other objects and features of this invention will more fully appear fromthe following detail description taken in connection with theaccompanying drawings, which illustrate several embodiments thereof, andin which:

Figure 1 is an enlarged fragmentary vertical sectional view showing thecontacts and associated parts of a circuit breaker embodying theprinciples of the present invention;

Figure 2 is an enlarged transverse fragmentary sectional view of thesame, taken substantially on line IIII of Figure 1;

Figure 3 is an enlarged fragmentary vertical sectional view showing theconstruction of one of 'the terminals of a single break circuit breakerembodying the present invention;

Figure 4 is a view in elevation showing a modifled arrangement 01' thepresent invention, wherein the circuit breaker is mounted in combinationwith a fuse;

Figure 5 is a side view of the same;

Figure 6 is another modified arrangement showing a single break circuitbreaker of the hereindescribed type mounted so as to form a hingedswitch blade which may be opened to effect a visible break in thecircuit;

Figure 7 is an enlarged fragmentary detail plan view showing the uppercontact of the switch blade;

Figure 8 is another modified arrangement wherein the present inventionis embodied in a double break circuit breaker;

Figure 9 is an alternative arrangement of Figure 8, to efiect a visiblebreak in the circuit;

Figure 10 is a detail view showing the contact rod utilized inconnection with the circuit breaker of Figures 8 and 9; and

Figure 11 is a fragmentary view partly in crosssection showing amodified lower end for the contact rod to facilitate improved operationof the circuit breaker.

As shown on the drawings:

Referring to the drawings, a preferred form of the present invention isshown in Figures 1, 2 and 3 as a single break circuit breaker. This formof the invention comprises in general a contact assembly, generallyindicated at A for initially interrupting the power circuit; and aterminal construction as generally indicated at B for completing theinterruption of the electrical circuit after the load interruptingcontacts have opened. v

Thecontact assembly A comprises a casting I! having one end of acylindrical'tube ii of organic material such as horn fiber supportedtherein. At one side, the casting I5 is shaped to define a chamber Hwhich houses a'portion of the contact mechanism. One wall of the chamberI1 is in the form of aplate or cover "Which may be secured in positionin any appropriate manner, but is preferably removably secured to enableaccess to'the contact mechanism. This wall is centrally provided with ascrew stud I! having a shank portion 20 which serves as a guide for acontact casting 2| having a stem portion 22 which is centrally aperturedat 23 to receive the shank 20 therein and permit axial movement of thecontact casting on the shank.

The contact casting 2! is mechanically and electrically connected to thewall I. by a pinrality of flexible spring connectors 24 of approximatelyhorseshoe shape. The inner face of the contact casting has acylindrical'extenslon 25, preferably of circular cross-section, axiallyalined with the stem 22 and slidably received in a lateral opening 26 inthe wall of the tube It. A contact member 21 of any appropriate materialis secured, by soldering or the like, to the inner end of the extension25 and is normally pressed towards the center of the tube 16 by a spring24 that surrounds the stem 22 and bears against the wall I! and theouter face of the contact casting 2|.

Diametrically opposite the opening 2.,is a similar opening 29a in thetube I for receiving a contact member 30 which is axially movablerelative to the opening 29a by an adjusting screw 3| to which it issecured and which is in threaded engagement with the casting ll. I

Within the tube l6, there is disposed a rod 32 of conducting material.At the upper end of this rod is an axially extending bolt 33 threaded atboth, ends, one end of this bolt being secured in the upper end of rod32 and the other end oi this bolt extending into and threadedly engagingan elongated member 34 of fibrous or other organic material, which formsan extension for the rod 32. "Clampingly secured between the extension34 and the rod 32 by means of the bolt 33 is an annular contact member35 which may also be soldered to the rod 32 in order to reduce theelectrical resistance of the joint. It will be noted that the rod 32,contact member I! and the extension 34 are of the same diameter so as tovirtually form a continuous rod, .and that the diameter is such that alimited clearance or annular shaped space is secured between the outersurface of the rod assembly and the inner surface of the tube Hi.

The extension 34 is of such length that when the contact 35 is engagedby the contacts 21 and 30. the extension extends beyond the upper end ofthe tube ii. The upper end of this extension may be of frusto-conicalshape as shown in Figure 1. It will be noted that the end faces of thecontact members 21 and 3| are not arcuate to conform to the cylindricalsurface of the movable concentrically surrounding the extension 24 tendto straighten out with a temperature rice. I I

and forming an extension of the tube I is an exteriorly threaded tubularmember 35 of metallic construction which is secured into the casting l5as by welding at 31 and provided with a plurality of slots 36a at itsouter, end. The member 36 is closed by means of a cap 33 so as to forma' chamber 39 which is in communication with the clearance space betweenthe rod assembly and the interior surface of the tube IS. The cap 38 isof larger diameter than the tube 36 and at its lower end is in threadedengagement with the exteriorly threaded surface of the tube .36, thisarrangement enabling variation of the size of the chamber 39 in a givensize unit to meet different operating conditions. While it has beenfound'that the ratio of the total volume of chamber 39 to the volumedisplaced by the rod 34, when the breaker is in the fully closedposition, may be varied without marked effect on the performance of thebreaker, it is preferable to use a ratio lying between 2 to 1 and 3 to 1for breakers that are to be used on a circuit carryf ing up toapproximately 1200 amperes at 5000 1 small size willquickly extinguishthe arc.

volts. The metallic wall of this chamber will, by quickly condensing thegases, serve to dissipate the heat of the arc.

In the arrangement described above, it will be apparent that in order toopen the contacts, the rod assembly may be moved downwardly and thatduring this movement the extension 34 serves as a follower to maintainthe arcing space, that is, the space between .the rod assembly and theinterior surface of the tube H5 at a constant value. Likewise, as theextension 34 moves out of the chamber 39, there is a decrease in thepressure within this chamber which acts to draw the are caused by thebreaking of the contacts into the arcing space where it is confinedbetween surfaces of fibrous or other organic material. Although I havedisclosed this means of causing the arc to travel upwardly relative tothe tube I6 from the contacts, the arc would travel in this directioneven though there were no decrease of pressure in the chamber 39 aswould be the case when the tubular member is open or not provided with acap 33. This movement of the arc would take place for the reason thatthe length of the arcing space belowthe contacts is of greater extentthan the arcing space above the contacts, in which case the latter wouldoffer less resistance to the arc and the arc would naturally take thiscourse.

As indicated above, the invention provides a dry type of circuit breakerwhich may be used in place of oil switcher and circuit breakers to opentransmission lines carrying heavy currents at high voltages. It isimpossible to prevent arcing when contacts are separated to interruptcurrent flow of the order of hundreds of amperes in, for example, a 5000volt transmission line, butcircult breakers of the described.costruction and of The surfaces of the tube and follower which aresubjected to the arc will be decomposed and emit gases which areeffective in setting up a violent turbulence and in causing deionizationof the arc and hence its extin'guishment.

Immediately below the contact 21, there is pro- 'vided in the wall ofthe tube IS a passageway M which connects the arcing space with thechamber 11. Where metal contacts are used, any

globules of metal which are formed when the contacts are separated underload, will be driven through this passageway into the otherwise closed.chamber 11 where they may solidify without interfering with the movementof the rod assembly.

Line connections, it will be obvious, may be made to any portion of thecasting 15. In the present instance I have shown the plate 18 beingextended to form a terminal generally indicated at 4|. The electricalcircuit would therefore be from the terminal 4| to the plate 18, theflexible connector 24 to the contact casting 2|, and also through theadjusting screw 31 to contact and thence from the contacts 21 and 30 tocontact 35 and the rod 32.

The load breaking contact unit is easily embodied in a variety ofarrangements. In the preferred and'more simple arrangement of theinvention, the circuit is completed, as shown in Figure 3, through theterminal B. This terminal comprises a cap 42 which is threadedly securedto the lower end of tube l6 and carries a lug 43 to facilitate making aline connection thereto. This cap is centrally apertured as shown at 44so as to enable the rod 32 to extend therethrough. Spring contacts 45are secured at one end in the cap 42 and are so arranged that the freeends thereof frictionally engage the rod 32 to thereby complete theelectrical circuit from the rod 32 to the cap 42 and lug 43, which isconnected to the line.

The rod 32 may be actuated by anyappropriate power means or, asdisclosed herein, the rod may be fitted at its lower end with a casting46 having a portion defining .an opening 41 for receiving an operatinghook, whereby the rod may be manually operated. The casting 46 is alsoshaped at its upper end to form a socket 48 to receive the free ends ofthe contact springs 45. The sides of this socket closely engage thesides of the springs 45 and serve to press them firmly against thecontact rod 32, thus preventingarcing. Moreover, the contact springs dueto their abutment with the bottom of the socket 43 also serve as a stopto limit the upward'movement of the rod assembly. If desired, a shield49 may be disposed around the contact springs and supported from the cap42 in any appropriate manner.

fuse 50 of the removable hinged type. The lower 3 end of the fuseelement is provided with a casting 51 which forms a terminal forengaging with contact clips 52. This terminal also forms one ofthe'hinge members and is provided with trunnions 53 which are adapted tobe removably supported in spaced bracket members 54-54. For effecting aremovable support for the fuse, the brackets are respectively providedwith openings 55 which are in communication with a U-shaped slot so thatthe trunnions 53 may be inserted in the openings 55 and moved into theU-shaped slot.

The upper end of the fuse carries a terminal 56 which is adapted toengage spring clips 51 sup- 90 having one end fixedly secured by a nutandbolt connection 9| to the insulator. This bolt and nut connectionalso secures a terminal lug front of the casting 63, whereby theoperator. 4c

that the trunnions 53 62 by means of which aline connection may be madeto the fuse element.

For disengaging the latch spring 69 so that the fuse maybe swung out ofcontact with the spring contact clip 51, there is provided a casting 63which is pivoted at and adapted to be engaged by an operating hook. Thiscasting has an arm 65 which extends beneath the latch spring so thatwhen the casting is engaged by the operating hook and a downward forceis exerted, the arm'65will raise the latch spring 60 so as to releasethe fuse and enable the operator to swing it out of contact with thespring clip 51. If desired, the fuse, after it has beenopened, may betotally. disengaged by moving it upwardly so are released from thebracket 54. 1

The lower terminal of the fuse is electrically connected through a stripof current conducting material 66 to the casting l5 of the circuitbreaker so that the complete circuit through the device would be fromlug 62 through contacts 51, the fuse, contacts 52, connector 66, castingl5, contacts 2'! and 30, contacts 35, and thence through rod 32 (Figure1), spring contacts 45 to lug 43.

In the foregoing arrangement, it would be very undesirable to open thefuse until after the circuit breaker contacts have been actuated to openthe load circuit. In order to prevent improper sequence of operation,the circuit breaker and fuse are interlocked so as to make it compulsoryto first open the circuit breaker before it is possible to open thefuse.

This is accomplished by mounting a barrier or shield 67 for pivotalmovement about a pivot member 68 supported at the upper end of thecircuit breaker on tube 38. This barrier is so disposed that when inlowered position it lies in cannot insert the hook therein to disengagethe latch 80 and thereby enable the fuse to be swung to open position.

It will be observed that the upper end of the tube 36 is, in thisinstance, left open so as to enable the extension 34 of the rod assemblyto project outwardly thereof when the circuit breaker is closed. In thisdesign the tube 36 is an integral extension of the tube 56, and in orderto produce, in this open ended design, somewhat the same gas confiningeffect as is produced in the closed-end design, the clearance betweenthe rod 3% and tube 36 is made as small as the clearance between the rod32 and the tube iii. For automatically moving the barrier to effectiveand ineffective positions in response to the closing and opening of thecircuit breaker, an arm 69 is secured to the barrier so as to extend atsubstantially right angles thereto and is so disposed as to be engagedby the extension 34 when the contacts of the circuit breaker are closed.Engagemerit-of this arm by the extension forces the bar-' rier to assumeeffective position to prevent opening of the fuse by the operator.Assuming that the circuit breaker is opened by pulling down on the rodassembly, the extension 34 is, moved downwardly and enables the rotationof the arm 69 and barrier 61 in a counter-clockwise directionunder theinfluence of a spring 10 to the position shown in dotted lines in Figure4 In this position of the barrier or shield, the fuse may be swung toopen position. 7

Another 'modification of the preferred-form of the hereindescribedinvention is disclosed in Figure 6, wherein the circuit breakerdisclosed 15 in Figures 1,2 and 3 is hingedly mounted for operation as aswitch blade so as to form a. visible break in the circuit.modification, an interlocking arrangement is provided which preventsopening the blade until the circuit breaker has been opened.Corresponding parts have been indicated by like numerals as heretoforereferred to in the description. The circuit breaker is hinged at itslower 'end by providing a pivot H on the cap 42, this cap beingidentical with the cap shown in Figure 3, except for the addition of thepivot. The entire assembly is made removable by supporting the pivotends in aligned slots Ha-Ha of a bracket 12 which is secured in theusual manner to an insulating support 73. The bracket 12 also serves asan electrical connection from the cap 42 to the associated circuitconnection lead. The cast- Moreover in this ing l5 instead of beingprovided with a terminal I the rod assembly, when swinging, the circuit0 breaker about the pivot H to disengage the contacts i4 and it. On theother hand, it will be seen that when the rod assembly is pulleddownwardly to open the circuit breaker and is entirely removed, thecircuit breaker is then free to be swung to form a visible break in thecircuit. This movement is accomplished by inserting a switch hook in anopening 19 which may be provided in the casting 55. Q

In Figures 8 and 9, the invention is shown as being embodied in amodified form covering a double break circuit breaker. In thisarrangement, two of the load breaking contact assemblies A-A areutilized. The construction of each of the contact assemblies is the sameas in the single break circuit breaker and each functions in the samemanner as previously described in connection with the description of thepreferred form of the invention. The only difference is that in thisarrangement, the rod as disclosed in Figure 10 is of fibrous materialwhich is made up of an end section as, a central section BI and an upperend section 82 which are separated by contact elements 83 and 84. Thesections and contacts are assembled to form in effect a single rod, a.bolt 85 extending through the central section and threadedly engaging atone end contact 84 and section 82 and at its other end contact 83 andsection 80. It will therefore be seen that this rod also performs theadditional function of forming an electrical connection between thecontacts Hand 84. The electrical circuit in this contact assembly tocontact 84, throughthe rod 85, contact 83, and thence to the casting l5of the lowermost contact assembly A.

As shown in Figure 9 this modification may alternatively arranged toform a visible break case would be from the casting I5 of the upper bythe simple expedient of forming an opening I or in other wordsdiscontinuing a portio'rTof'tli tube l5 lying between the upper andlower contact unit. In the alternative arrangement, when the rod isentirely withdrawn, a visible break is farmed between the contact units.

:In Figure 11, an alternative arrangement is shown for the member to beengaged by the switch hook in opening the breaker. In this arrangementinstead of having a rigid connection with the rod 32, the sleeve 86 isprovided within which there is reciprocably mounted a pull member 81which is arranged at its lower end with an opening 88 for engagement bya switch hook. The upper end of the member 81 is connected 'to one endof a coil spring 89 which is anchored at its other end to the rod 32.This arrangement,

moved with slower movement to withdraw the same from the breaker. Thisarrangement has been found to be much more effective than where the rodis initially moved by a direct pull with the switch hook.

From actual tests which have been made upon circuit breakers embodyingthe hereindescribed invention, it has been found that the best resultsare attained when the difference between the outside diameter of the rod32 and the interlor diameter of the tube ii are between of an inch anda; of an inch. With the lower limit, small metal particles thrown oilfrom the con tact under the influence of the arc will not besuiliciently large to cause the rod to jam. Of course, most of theseparticles will be ejected through the opening 40, but some of them mayremain in the space between the rod and the surrounding tube. If thelimit is made greater than a l of an inch there will be a tendency forthe ionized gases to be discharged through the lower end of the tube It.

From the foregoing description, it will be apparent that this inventionprovides a novel circuit breaker of the dry type, which has excellentarc extinguishing characteristics, which may also be utilized not onlyas a circuit breaker but as a disconnecting device; which is economicalto construct and which may be embodied in a variety of combinations.

Now, it is of course to be understood that although I have described indetail several embodiments of my invention, the invention is not to bethus limited but only insofar as defined by the scope and spirit of theappended claims.

I claim as my invention:

1. A circuit breaker comprising a tubular member of organic material, arod of similar material mounted for longitudinal movement within saidmember and having its surface inwardly.

spaced from the inner wall of said member to ,form an arc-extinguishingchamber, cooperative electrical contacts respectively associated withsaid member and rod and adapted to open and close an electrical circuitin response to the movement of said rod, and means responsive to acircuit-opening movement of said rod for decreasing pressure at one endof said tube.

2. A circuit breaker of the character described comprising a cylindricalchamber including tubular member of organic material adapted to emit anarc extinguishing medium under the influence of anelectric ate, ametallic rod mounted for longitudinal movement within said tubularmember, cooperable contacts respectively. associated with said rod. andmember, the

contact associated with the tubular member being located intermediatethe ends of said chamber, and a smooth walled cylindrical element ofmaterial similar to that forming the tubular member extending from andmovable simultaneously with the rod, said element being spaced from theinner surface of said tubular member, whereby an are formed by theseparation of said contacts will impinge upon the opposed surfaces oforganic material of said tubular member and rodlike element. v l

3. A circuit interrupting device of the character described comprisingrelatively movable contacts, means contiguous said contacts defining anarcing space of constant volume and adapted under the influence of anarc to emit an arc extinguishing medium, means forming a closedexpansion chamber for said medium in communication with said arcingspace, and means whereby the volume of said chamber may be varied toadopt the device for different. conditions of operation.

4. A circuit breaker comprising a pair of contacts, means for eil'ectingrelative movement of said contacts to engage and alternatively toseparate the same, means forming an annular arc extinguishing chamberwhich extends in opposite directions from said contacts and retains asubstantially constant cross-section during relative movement of saidcontacts, said chamber metal member in axial alinement, arod ofinsulating material mounted for reciprocating movement in said tubularmembers, contact means carried by said member of insulating material atthe end thereof adjacent the metal member, and contact means on andspaced from the ends of said rod, said rod having a continuouscylindrical outer surface of less diameter than the bore of .saidtubular members to provide an .arc extinguishing chamber of annularcross-section.

6. A circuit breaker as claimed in claim 5, wherein said rod has adiameter of the order of 3 2 inch less than the bore of the tubularmember.

7. A circuit breaker as claimed in claim 5, wherein said first contactmeans comprises a metallic casing into which one end of said tubularmember is secured, a contact movably supported by said casing andextending into a transverse bore in said tubular member, and springmeans pressing said contact towards the interior of the center of saidtubular member.

8. In a circuit breaker, a tube of insulating material, alinedtransverse openings through said tube, contacts mounted in said openingsand positioned with respect to the portion oi the contact that isengaged by said contact memher. i i

10. A circuit breaker comprising a tubular member of insulatingmaterial, contact means extending into the bore of said member at aregion spaced from the ends oi said member, a rod of insulating materialextending into said tubular member, contact means on said rod forcooperation with the contact means of said tubular member, said rodbeingof less diameter than the bore of said tubular member and including anextension movable into transverse alinement with the contact means ofsaid tubular member when the rod is displaced to separate the re-.

spective contact means, and a vent openingilatorally through the wall ofsaid tubular member adjacent the contact means thereof, said ventopening being positioned at that side of said contact means towardswhich the contact means of said rod is moved to separate the respectivecontact means.

-11. A circuit breaker comprising relatively separable contacts,wall-forming means contiguous said contacts defining an arcing space ofconstant cross-section extending in opposite di= rections from saidcontacts when engaged and during separation thereof, and means forpositively reducing the pressure at one end of said space upon theseparation of said contacts to elongate the resultant arc and extend thesame into said space, said wall-forming means comprising materialadapted when subjected to an arc to evolve an arc extinguishing medium.

12. A circuit breaker comprising a tubular member of insulating materialcapable of vaporizing to produce an arc-extinguishing medium,

terminal contact means spaced from the ends of mg section having asmooth cylindrical wall spaced from the inner wall of said member by anannular gap having a radial length of the order of a inch. t

13. A circuit breaker as claimed in claim 12, 1

wherein said tubularmember has a restricted opening extending laterallythrough the wall thereof adjacent said terminal contact means and at theside thereof where an arc is formed when the electrical connection isbroken.

GEORGE A. BEAmi-IEVVS.

